1. Field of the Invention
The present invention relates to a threaded union highly resistant to overtorque and compression that is used with unions that connect tubular members, particularly not exclusively, this union is used with pipes that transport liquids or pressurized gases such as steam, gas or petroleum, and is used with exploration columns or in the production of gas, or petroleum, or used with pipe lines that conduct liquids or gases.
2. Description of the Related Art
Among the main types of connections used today for the above-mentioned purposes includes one female member having one internal circumferential surface provided with a thread and a male member having one external circumferential surface also provided with a thread that corresponds to the female thread, and where the male member is received into the female member through the screwing process. The free edge of one of the members (generally the male) called nose has an annular surface radially oriented, which is pressed against a corresponding surface of the other member (shoulder of torque). In these types of connections there may or may not exist another surface directed axially in the free extreme of one of the members that functions as a seal when pressing itself against a corresponding surface directed axially on the other member. The annular surfaces radially oriented remain compressed as a result of the assembly of the connection. The maximum torque that the connection is able to absorb is limited by the dimensions and design of the free extreme of the first member and of the shoulder of torque zone. Present time connections have similarities between the dimensions of the radially oriented surface of the free extreme of the male member and the corresponding surface of the female member, as well as between the area of resistance of the nose and the area of resistance of the shoulder. However, when torque is increased to present-time connections during assembly or subsequently during any operation with the assembled column, the combination of tensions produced in the shoulder of torque favor the development of stress that shears the material and provokes rupture of the shoulder, thus creating a weak point or critical zone in the connection because of torsional stress. To improve the performance of the connection with this type of stress, it is a common practice to increase the thickness of the nose and the thickness of the shoulder of torque in a similar manner, thus increasing the overtorque bearing power. However, this also increases the susceptibility of the seal to generate seizing, due to greater rigidity of the nose and consequent increase of contact pressures. In addition, increasing the thickness of the nose requires adjustment of the free extreme of the pipe before threading. This affects the properties of the material and complicates the manufacturing process.
The primary object of the present invention is to provide an improved pipe connection that eliminates or reduces the disadvantages of the present state of the art mentioned above, such as premature failure of the shoulder of torque, while at the same time, increasing the connection""s capability to carry torsional stress.
It is also the purpose of the present invention to provide pipe connections where the contact pressure of the sealing surfaces is maintained limited, thus reducing the risk of seizing being generated.
Another purpose of the invention is to provide a union able to maintain stable the shape of the flow line of the fluid that circulates internally without causing substantial changes.
To accomplish the aforementioned objectives, the pipe connection of the present invention comprises a female member having a circumferential internal surface provided with a thread, and a male member having an external circumferential surface also provided with a thread that corresponds to that of the female member. The male member is received into the female member through the screwing process, whereby the members are coupled. One annular surface generally radially oriented located on the free extreme of one of the members, called nose, makes firm contact with an opposite annular surface generally radially oriented toward the other member and named shoulder of torque. The annular surface radially oriented of the first member is intersected in its minor diameter by the interior surface of the pipe. Alternatively, it intersects an internal cylindrical surface parallel to the axis of the pipe. Alternatively, it intersects a trunco-conical in shape surface which, at the same time, intersects the internal surface of the pipe, while the annular surface radially oriented of the second member intersects on its minor diameter with a trunco-conical shape surface radially oriented forming angle B which is between 5xc2x0 and 25xc2x0 with the axis of the pipe. This surface, at the same time, intersects with an internal cylindrical surface parallel to the axis of the pipe. Alternatively it forms an angle of less than 5xc2x0 with the same.
The shoulder of torque configuration, according to the present invention, allows greater overtorque capability of the union, by increasing the section of resistance of the shoulder torque in the plane where the main shear tensions, responsible for the failure in the mechanism in the conventional unions, are generated. Thus, substantially improving the resistance of this weak zone in the commonly used joints. This improvement in resistance is obtained without increasing the thickness of the nose, and without increasing susceptibility to seizing when the nose has a sealant surface of metal to metal contact.
According to a configuration, the first member corresponds to the male member, with a surface generally radially oriented forming angle A with the perpendicular plane to the axis of the pipe in the male member making contact under pressure with a corresponding surface generally radially oriented and forming angle A with the perpendicular to the axis of the pipe in the female member.